Issue notifications all use the same message id, resulting in dropped emails

We are not receiving all email updates to issues in your issue tracker. We have investigated this and the cause seems to come down to duplicated message id's.
Normally all emails have a unique message id, and many mail servers have a filter on them which prevents messages with the same id being delivered multiple times to an individual.

It seems that when issues on BitBucket are updated, the update emails for a particular issue are sent out with the same id, which means that our email system only delivers the first one. Please could you investigate and see whether this behaviour can be altered so that all update emails get unique ids.

As an example, we created this issue. We added 2 updates to it, and between them, we changed Stuart's email address to a different LShift account, which allowed us to avoid the email being dropped due to duplication.

We then examined the headers which are included below. You can see that the Message ID is the same in both messages, which should not happen.